1. Field of the Invention
The present invention relates to a semiconductor laser device using a compound semiconductor material and, more particularly, a semiconductor laser device having a current blocking region in end face portions (facet portions) thereof in a resonator direction.
2. Description of the Related Art
In recent years, a semiconductor laser emitting a light of a short wavelength has been developed to be applied to a high-density optical disk system, a high-speed laser printer, a bar code reader, and the like. Under these circumstances, an InGaAlP laser having an oscillation wavelength in a 0.6-.mu.m band (red region) and a GaAlAs laser having an oscillation wavelength in a 0.8-.mu.m band (infrared region) have received a great deal of attention as a promising semiconductor laser emitting a light of a short wavelength. In addition, a high-output laser having a 30-mW output has been strongly demanded to be mainly applied to the field of optical disks or the like.
In order to answer the above demands, in recent years, a laser having a window structure for rendering the facet portions transparent to an oscillation wavelength, and a laser having a current blocking structure in which a current blocking region is formed in the facet portions have been proposed.
Since the facet portions in the laser having the window structure is transparent to the oscillation wavelength, COD (Catastrophic Optical Damage) caused by an increase in temperature of the facet portions can be prevented, and a very high output can be expected. For this reason, the technique of the laser having the window structure is regarded as an important technique required for realizing a 30-mW output and simultaneously realizing a high output and emission of a light of a short wavelength. However, complicated processes are required for manufacturing this laser.
On the other hand, the laser having the current blocking structure can be manufactured by relatively simple processes, and a high output can be expected by the following effect. An increase in temperature of facet portions of the laser is suppressed to suppress the recombination of carriers in the facet portions. However, the number of excited carriers in a current blocking region in the facet portions of the laser is less than the number of excited carriers in an injection region, and the bandgap of the facet portions are actually decreased. For this reason, the facet portions absorbs light having the oscillation wavelength, and a COD level is decreased, thereby disadvantageously limiting a high-output operation.
As described above, in a semiconductor laser having a conventional current blocking structure expected as a promising high-output semiconductor laser, the bandgap of an active layer in the facet portions are actually decreased to cause a decrease in COD level, thereby disabling a sufficiently high output.